[llvm] [RISCV][TTI]Use processShuffleMasks for cost estimations/actual per-register shuffles (PR #118103)

[Alexey Bataev via llvm-commits]

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@@ -388,7 +388,109 @@ InstructionCost RISCVTTIImpl::getShuffleCost(TTI::ShuffleKind Kind,
   // First, handle cases where having a fixed length vector enables us to
   // give a more accurate cost than falling back to generic scalable codegen.
   // TODO: Each of these cases hints at a modeling gap around scalable vectors.
-  if (isa<FixedVectorType>(Tp)) {
+  if (ST->hasVInstructions() && isa<FixedVectorType>(Tp)) {
+    MVT LegalVT = LT.second;
+    InstructionCost NumOfDests = InstructionCost::getInvalid();
+    const auto VLen = ST->getRealVLen();
+    if (VLen && LegalVT.isFixedLengthVector() && !Mask.empty()) {
+      MVT ElemVT = LegalVT.getVectorElementType();
+      unsigned ElemsPerVReg = *VLen / ElemVT.getFixedSizeInBits();
+      LegalVT = getTypeLegalizationCost(
+                    FixedVectorType::get(Tp->getElementType(), ElemsPerVReg))
+                    .second;
+      NumOfDests = divideCeil(Mask.size(), LegalVT.getVectorNumElements());
+    }
+    if (NumOfDests.isValid() && NumOfDests > 1 &&
+        LegalVT.isFixedLengthVector() &&
+        LegalVT.getVectorElementType().getSizeInBits() ==
+            Tp->getElementType()->getPrimitiveSizeInBits() &&
+        LegalVT.getVectorNumElements() <
+            Tp->getElementCount().getFixedValue()) {
+      unsigned VecTySize = DL.getTypeStoreSize(Tp);
+      unsigned LegalVTSize = LegalVT.getStoreSize();
+      // Number of source vectors after legalization:
+      unsigned NumOfSrcs = divideCeil(VecTySize, LegalVTSize);
+      // Number of destination vectors after legalization:
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alexey-bataev wrote:

Yes, fixed

https://github.com/llvm/llvm-project/pull/118103